Date of Award
Master of Science (MS)
Dr. Vincent Richards, Committee Chair
Dr. Barbara Campbell
Dr. Gary LeCleir
Man-made water systems can have complex microbial communities. Legionella spp. are ubiquitous in these environments and, with favorable conditions, can lead to outbreaks of Legionnaires disease. Included in these water systems are free living amoebas (FLA) and potential other eukaryotes that may act as a reservoir for Legionella survival and replication. Associations with these hosts can play a role in Legionnaires' disease outbreaks. A water cooling tower in Aikens, SC associated with L. pneumophila was measured every month for environmental parameters (temperature, bromine (Br), chlorine (Cl), pH, and dissolved oxygen). Water and sediment samples were collected every week for six months (March-August 2016). Samples were sequenced using 16S rRNA and 18S rRNA gene primers and analyzed to understand the bacterial and eukaryote community dynamics and their association with environmental parameters and correlations among bacteria and eukaryotic taxa.
The genus Legionella was found to be positively correlated in microbial association networks with Vermamoeba vermiformis, Vannella, Bilateria, other eukaryotic groups (Streptophyta, ConTHREEp and Gregarinasina), and numerous bacterial genera including Halomonas, Candidatus Protochlamydia, and Candidatus Xiphinematobacter. These correlations could indicate a commensal or predator-prey relationship among the eukaryotes and a similar host/lifestyle mechanism as Legionella. However, there was no correlation with Acanthamoeba, a common host of Legionella spp., potentially due to the crash in this amoeba population after April. The main environmental parameter that was correlated with changes in the bacterial and eukaryotic community composition was temperature. The bacterial community showed a stronger response to the environmental parameters than the eukaryotic community as seen by the changes in community richness as well as the significant differences between the bacterial communities in spring and summer months. In response to seasonal changes, there were major seasonal taxonomic changes from spring months (March-April) to summer months (May-August). Beta diversity was significant between summer and spring months for the bacteria but not significant for the eukaryotes. Though, Streptophyta (plant clade) and ediment during the spring, but transitioned to being most prevalent in the water during the summer. Whereas, majority of the eukaryotes were most prevalent in the water during the spring and became more prevalent in the sediment during the summer. Further understanding of the different dynamics between water and sediment should be explored.
This study, to our knowledge, provides the first characterization of the bacterial and eukaryotic community of a cooling tower known to have L. pneumophila in relation to environmental parameters. Understanding the community dynamics of water cooling tower associated Legionella spp. can provide insight into the development of Legionnaires' disease by characterizing new host associations and bacteria with similar lifestyles.
Hammer, Emily, "Temporal and Ecological Community Dynamics of Water-Cooling Tower Associated Legionella spp." (2018). All Theses. 2938.